Adjustable resistance



July 9, 1935. E R STQEKLE 2,007,462

ADJUSTABLE RESISTANCE Filed Aug. 1, 1931 INVENTOR.

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ATTORNEYS Patented July 9, 1935 OFFICE accuse Anrnsraerr.

Application August 1,

iii (Claims.

This invention relates to an improvement in electrical resistances particularly of the types adjustable from low values of resistance to ve y high values of resistance.

It is practical to make such resistances of a carbonaceous or graphite coating upon a suitable base but it is. undesirable to subject resistances of this character to the direct action of the usual sliding or rubbing form of contact for the reason that this action changes the resistance in an uncontrolled and undesirable manner.

in my prior Patent 1,653,745, granted December 27, 1927, and. 1,704,154, granted March 5, 1929, as well as in Patent 1,660,879, granted February 28, 1928, there are shown several different forms or structures of contact members which avoid excessive rubbing of the adjustable contact upon the resistor. Basically, these several patents disclose the idea of a contact member which does not subject the resistor element to an undesirable rubbing or abrading action.

One of the principal objects of the present invention is to provide a novel structural organization embodying the advantages of the structures shown in said patents and of such character as to lend itself readily to standard manufacturing processes and methods While being especially easy to assemble. The feature of having a contact member which avoids undesirable rubbing or abraiding action on the resistor is preserved and yet the resistor and the adjustable member controlling the value thereof are all mounted within a housing which serves not only as an enclosure but also as a mounting for the resistor and for the other elements of the structure. This advantage is had with extreme simplicity in construction.

More particularly, the present invention makes it practical to fabricate the resistance element in the form of a straight ribbon or strip which is afterwards bent into circular form and conveniently inserted within a correspondingly shaped portion of the housing. The assembly is such that the resistor tends to hold itself in position in the housing without the necessity of utilizing an adhesive or fastening means. This type of interconnection between the housing and resistor is advantageous in many respects. For example, it provides for the ready substitution of one resistor for another. By originally constructing the resistor in the form of a straight strip their manufacture is rendered easier and le expensive for the reason that in such form the resistor may be more conveniently coated with graphite than it could he were it of annular 1931, Serial No. Swill-7% (Cl. 2l-55) formation. Another advantage resides in having the adjust-able pressure means carried by the cap and susceptible of removal, adjustment, replacement or repair Without disturbing the assembly of the parts in the main housing.

Other objects and advantages reside in certain novel features of the construction, arrangement and combination of parts which will be hereinafter more fully described and particularly pointed out in the appended claims, reference being 10 had to the accompanying drawing forming a part of this specification, and in which:

Figure 1 is a view partly in central vertical longitudinal section and partly in side elevation showing an adjustable resistance embodying the present invention;

Figure 2 is a view in end elevation looking toward the right in Figure l, and having parts broken away and parts shown in section for the sake of illustration; and

Figure 3 is a detail perspective View of the flexible conductor.

Referring to the drawing, the numeral i designates generally a cup-shaped casing or housing consisting of a cylindrical portion 2, a back plate 3 and a tapered connecting portion 4. The enclosure provided by the housing is completed by a flanged cap or cover 5 which has its flange fitted or telescoped over the cylindrical portion 2 of the housing and releasably held in such position by means of securing lugs 6 which, in the assembly, are bent around into secure engagement with the housing.

An annular strip l of insulating material lines the cylindrical portion 2 of the housing. Fitted 5 against the inner surface of the strip l is a resistor 8 also in the form of a strip and in the assembly curved or bent in the form of an approximately complete annulus. With this construction the resistor or resistant element may be and preferably is made in the form of a straight ribbon or strip and bent in the form of an annulus just prior to its insertion in the base. As the resistor may be originally manufactured in the form of a strip its production is simplified and rendered less expensive for the reason that the straight ribbon or strip can be more conveniently coated with graphite or the like than annular resistors. Furthermore, the resistor when so constructed, tends, due to its inherent resiliency, to hold itself in position in the casing and under some circumstances it is not necessary to employ any fastening device for securing it in proper position in the assembly. However, it may be securely held by the same means employed for fastening its terminals thereto. For example, as shown in the drawing, the terminals 9 and i0 provided at the ends of the resistor 8 may be formed with angular portions 9 and ID at their inner ends,

which portions are engaged with'the ends of the resistor 8 and firmly clamped in this position. To effect this clamping a bolt and nut l I coacts with a tongue I! formed by slotting the casing and.

with a clamping plate I3. The clamping plate l3 preferably does not directly engage the terminals but exerts its clamping action through an insulating strip Id. The ends of the clamping plate l3 may be inwardly turned as at l9 to provide stops. The flange of the cover 5 is cut away to accommodate the bolt and nut H and the terminals 9 and IE.

Coacting with the inner surface of the resistor 8 is a flexible conductor 20 also in the form of a practically complete annulus or ring and positioned within the confines of the resistor, that is, so positioned that its convex surface is disposed in operative relation to the inner concave surface of the resistor. The ring or annulus 29- is of less diameter than the resistor 9 and is so supported and constructed as to tend by virtue of its positioning and inherent resiliency to remain out of contact with the resistor. The support of the flexible conductor 20 is preferably effected by means of a' spider designated generally at 2| and including an apertured hub 22 having arms 23 integral therewith and with the edge of the ring 29. The apertured hub 22 is fastened by means of a rivet or bolt and nut 25 to the central portion of the back plate 3 of the casing l. Suitable insulating washers designatedat 29 and 27 are interposed between the hub 22 and the back plate 3 and these washers also insulate the rivet or bolt and nut 25 from the back plate of the casing. The head of the bolt and nut 25 serves to fasten the terminal 29 to the rivet, this terminal being electrically connected through the rivet with the flexible conductor.

Means is provided for flexing the conductor 29 into contact with the resistor progressively throughout the length of the conductor and in such manner as to avoid a rubbing or sliding contact between the conductor and the resistor. This means preferably consists of a rotatable shaft 39 supported for rotation in a bushing 3| securedto the cover 5 and adapted by its external threading for connection to a panel. On its outer end the shaft 90 has a knob 32 fixed thereto whereby it may be turned. The reduced inner end of the shaft extends through a transverse opening in a radial arm 33. A set screw 36 is threaded through an opening provided therefor in the arm 33 and has clamping engagement with the inner end of the shaft 30 to secure the radial arm to the shaft and constrain these parts to rotate together. The outer end of the radial arm 33 is provided with a longitudinal opening or socket 35 which slidably receives the shank of a headed pressure member designated generally at 36 and preferably consisting of a stud-like member of wood or other similar insulating material,

- the head of which is rounded to insure easy travel over the flexible conductor. A spring 39 biases the pressure member 36 to extended position in which it bears against the conductor 20 and flexes it into engagement with the resistor 8.

An adjustable resistance embodying the present invention may be connected in a circuit so that current flowing in through the terminal 28 will pass through the rivet or bolt and nut 25 and into the flexible conductor 20. At the point where the conductor 20 is flexed into the contact with the resistor 8, the current enters the resistor, passes therethrough and emerges at either the terminal 9 or [0, depending upon which is connected to the source of potential. The resistance between the terminal 28 and either of the terminals 9 and [0 will be varied as the location of the contact between conductor 20 and the resistor 8 is varied. If a potential diiference be applied between the terminals 9 and In any portion of this potential may be obtained between the terminal 28 and either of the terminals 9 and it. 'This reference to the mode of incorporating the adjustable resistance in the circuit is merely for the purpose of illustration.

The advantages of the present invention reside in the features of the structural organization which enable the resistance to lend itself to economical and easy manufacture, which endow it with reliability and durability, while preserving the advantage of a controlled range of resistance values. In particular, an outstanding advantage of the invention is the organization with a cylindrical or an equivalently shaped portion of the casing of a correspondingly formed resistor which is fitted within the casing so as to be housed as well as mechanically supported thereby. The flexible conductor is organized with the casing and with the resistor to engage the inside or concave surface of the resistor and the present means utilized for flexing the conductor into engagement with the resistor at any points throughout the extent of the latter is carried by the cover or cap. By so mounting the adjustable pressure means it is independent of the parts within the housing in so far as removal and replacement is concerned, and thus may be taken out, repaired, adjusted or replaced without disturbing the assembly of the parts in the main housing. This pressure means also coacts with the inside or concave surface of the flexible conductor and displaces or flexes the conductor outwardly in any adjustment. At the limits of its movement the pressure means is arrested against further'inovement by the action of the stop lugs l5.

It is to be understood that while one embodiment of the invention has been shown for the sake of illustration, that various changes in the size, shape and arrangement of the parts may be made without departing from the spirit of the invention or the scope of the subjoined claims.

The invention claimed is:

1. In a device of the character described, a housing having a cylindrical portion and a back plate connected thereto, a resistor in the form of an annulus fitted within and insulated from the cylindrical portion of the housing, a spider-like flexible conductor carried by and secured to the back plate of the housing by a connecting portion secured to said back plate, said conductor also having a split band-like contact strip located within the resistor and arms connecting the strip with the connecting portion of the conductor, said back plate being laterally offset from the cylindrical portion of the housing, and said arms extending at an inclination to the strip for supporting the same in spaced relation to the resistor 2. In a device of the character described, a housing having a cylindrical portion, a resistor in the form of a split annulus fitted within and insulated from the cylindrical portion of the housing, terminals at the ends of the resistor pro- ,iecting exteriorly of the housing through openings in the cylindrical portion of the housing between the peripheral edges thereof, and clamping means common to the terminals and engaging the housing and the terminals for securing the terminals to the resistor and the resistor through the terminals in the housing.

3. In a device of the character described, a housing having a cylindrical portion, a resistor in the form of a split annulus fitted within and insulated from the cylindrical portion of the housing, terminals at the ends of the resistor projecting exteriorly of the housing through openings in the cylindrical portion of the housing between the peripheral edges thereof and having portions overlapping the inner surface of the resistor, and clamping means common to the terminals and engaging the housing and the overlapping portions of the terminals for securing the terminals to the resistor and the resistor through the terminals in the housing.

4. In a device of the character described, a housing having a cylindrical portion, a resistor in the form of a split annulus fitted within and insulated from the cylindrical portion of the housing with the ends of the resistor in circumferential spaced relation, terminals at the ends of the resistor projecting exteriorly of the housing through the gap between the spaced ends of the resistor and through openings in the cylindrical portion of the housing between the peripheral edges thereof, said terminals having angularly bent inner ends overlapping the inner surface of the resistor, and means including a clamping plate spanning the gap between the angular inner ends of the terminals and the spaced ends of the resistor and engaging the inner ends of the terminals for securing the terminals to the re" sistor and the resistor through the terminals in the housing. 7

5. In a device of the character described, a housing having a cylindrical portion, a resistor in the form of a split annulus fitted within and insulated from the cylindrical portion of the housing with the ends of the resistor in circumferential spaced relation. terminals at the ends of the resistor projecting exteriorly of the housing through the gap between the spaced ends of the resistor and through openings in the cylindrical portion of the housing between the peripheral edges thereof, said terminals having angularly bent inner ends overlapping the inner surface of the resistor, a clamping plate spanning the .gap between the angular inner ends of the terminals and the spaced ends of the resistor for securing the terminals to the resistor and the resistor through the terminals in the housing, and fastening means engaging the plate and the cylindrical portion of the housing between the spaced ends of the resistor for drawing the plate into clamping relation with respect to the terminals and the resistor.

6. In a device of the character described, a housing having a cylindrical portion and a back plate connected thereto, a resistor in the form of a split annulus fitted within and insulated from the cylindrical portion of the housing with the ends of the resistor in circumferential spaced relation, terminals at the ends of the resistor projecting exteriorly of the housing through the gap between the spaced ends of the resistor and ning the gap between the bent ends of the terminals and the spaced ends of the resistor for clamping the terminals to the resistor and the resistor through the terminals in the housing, a flexible conductor secured to and carried by the back plate of the housing and having a band like contact strip located within and slightly spaced from the inner surface of the resistor, a cover for the housing opposite the back plate, and adjustable pressure means carried by the cover and operable against the inner surface of the conductor strip for flexing it outwardly into contact with the resistor at any point in its circumferential extent, said contact strip being secured in the housing against rotation and having its ends in juxtaposition to the clamping plate and terminating short of he same.

7. In a device of the character described, a housing having a cylindrical portion and a back plate connected thereto, a resistor in the form of a split annulus fitted within and insulated from the cylindrical portion of the housing with the ends of the resistor in circumferential spaced relation, terminals at the ends of the resistor projecting exteriorly of the housing through the gap between the spaced ends of the resistor and through openings in the cylindrical portion of the housing between the peripheral edges thereof, said terminals having angularly bent inner ends overlapping the inner surface of the re sister, means including a clamping plate spanning the gap between the bent ends of the terminals and the spaced ends of the resistor for clamping the terminals to the resistor and the resistor through the terminals in the housing, ajiexible conductor secured to and carried by the back plate of the housing and having a bandli-ke contact strip located within and slightly spaced from the inner surface of the resistor, a

cover for the housing opposite the back plate,

and adjustable pressure means carried by the cover and operable against the inner surface of the strip for flexing it outwardly into contact with the resistor at any point in its circumferential extent, said contact strip being secured in the housing against rotation and having its ends terminating short of the bent end of the termirials and the clamping plate, said clamping plate being disposed within the resistor to be in the path of rotation of the pressure means to provide stops therefor.

8. In a device of the character described, a support having a cylindrical portion and a transverse portion connected with and spanning the cylindrical portion on one side thereof, a resistor in the form of an annulus fitted within and insulated from said cylindrical portion, a conductor having a split annular-like contact strip and means connecting the strip to the transverse portion of the support at a location within the circumference of the strip, said connecting means holding the strip within the resistor in normally spaced relation thereto and against bodily and rotary displacement with respect to the resistor, said connecting means being flexible whereby the strip may be pressed into electrical contact with the inner surface of the resistor, and rotatable pressure means operable on the inner surface of the strip for pressing it into contact with the resistor at a variable location along the circumferential extent of the strip.

9. In a device of the character described, a support having a cylindrical portion and a transverse portion connected with and spanning the cylindrical portion on one side thereof, a resistor in the form of an annulus fitted within the cylindrical portion and insulated therefrom, a conductor having a split annular-like contact strip and means connecting the strip to the transverse portion of the support within the circumference of the strip, said connecting means holding the strip within the resistor in normally spaced relation thereto and against bodily and rotary displacement with respect to said resistor, said connecting means being flexible where by the strip may be pressed into electrical contact with the inner surface of the resistor, and rotatable pressure means located within the strip and operable on the inner surface thereof for pressing the strip into contact with the resistor at a variable location along the circumferential extent of the strip, said connecting means being disposed between the strip and the transverse portion of the support to which the strip is connected to be out of the path of rotary movement of said pressure means.

10. In a device of the character described, a

support having a cylindrical portion and transverse portions connected with and spanning the cylindrical portion on opposite sides thereof, a resistor in the form of an annulus fitted within and insulated from said cylindrical portion, a member rotatably supported by one of the transverse portions of the support and disposed for rotation within the resistor on an axis substantially parallel to the inner contact surface thereof, a conductor having a split annular-like contact strip. and means connecting the strip to the other of the transverse portions of the support at a point substantially opposite the axis of rotation of the rotary member, said connecting means holding the strip within the resistor in normally spaced relation thereto and against bodily and rotary displacement with respect to said resistor, said connecting means being flexible whereby the strip may be pressed into electrical contact with the inner surface of the resistor, and pressure means carried by the rotary member and engageable with the inner surface of the strip for flexing it outwardly into contact with the resistor.

ERWIN R. STOEKLE. 

